US3742358A

US3742358A - Tethered airborne communications and information transfer system

Info

Publication number: US3742358A
Application number: US00102597A
Authority: US
Inventors: R Cesaro
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-12-30
Filing date: 1970-12-30
Publication date: 1973-06-26
Anticipated expiration: 1990-06-26
Also published as: DE2327498A1; FR2234719A1; DE2327498C2; GB1431485A

Abstract

A tethered balloon including means for controlling the height thereof is utilized as an airborne platform for transmitting and receiving apparatus including a multiple antenna assembly. The antenna assembly is suspended from a gimbal or ball joint configuration attached to the balloon so that it is gravity stabilized in the vertical plane. The antenna assembly itself is comprised of a plurality of independently rotatable coaxial shafts having respective antenna means coupled thereto. The shafts are hung from a pendulum arm member which is freely moveable within a vertical cone angle limit of 45* and maintains vertical orientation to within + OR - 2*. The rotation of each of the coaxial shafts is independently controlled from a ground station by means of a control signal to selectively point each antenna means in a predetermined compass direction. Additionally, each coaxial shaft couples respective transmitter-receiver means to its antenna means in order to provide selective signal transfer between the ground station and/or other similar airborne systems.

Description

United States Patent [191 Cesaro June 26, 1 973 TETHERED AIRBORNE COMMUNICATIONS AND INFORMATION TRANSFER SYSTEM Richard S. Cesaro, 6264 Clearwood Road, Bethesda, Md. 20015 Filed: Dec. 30, 1970 App]. No.: 102,597

[76] Inventor:

[52] US. Cl 325/3, 325/4, 325/5,

[5 6] References Cited UNITED STATES PATENTS 4/1962 Katzin 325/4 11/1961 Rose 343/758 2/l960 Lanctot et al. 343/7565 Primary Examiner-Albert J. Mayer Attorney-Brady, OBoyle & Gates ABSTRACT A tethered balloon including means for controlling the height thereof is utilized as an airborne platform for transmitting and receiving apparatus including a multiple antenna assembly. The antenna assembly is suspended from a gimbal or ball joint configuration attached to the balloon so that it is gravity stabilized in the vertical plane. The antenna assembly itself is comprised of a plurality of independently rotatable coaxial shafts having respective antenna means coupled thereto. The shafts are hung from a pendulum arm member which is freely moveable within a vertical cone angle limit of 45 and maintains vertical orientation to within :2. The rotation of each of the coaxial shafts is independently controlled from a ground station by means of a control signal to selectively point each antenna means in a predetermined compass direction. Additionally, each coaxial shaft couples respective transmitter-receiver means to its antenna means in order to provide selective signal transfer between the ground station and/or other similar airborne systems.

13 Claims, 14 Drawing Figures 36 col/gm CONTROL TETHERED AIRBORNE COMMUNICATIONS AND INFORMATION TRANSFER SYSTEM BACKGROUND OF THE INVENTION 2. Field of the Invention This invention relates generally to electronic communications and information transfer systems and more particularly to a free space system incorporating an airborne antenna system capable of radiating and receiving electromagnetic energy over relatively long ranges and large earth areas in order to meet specific geographic application requirements.

2. Description of the Prior Art The concept of removing radiating and receiving antenna systems from ground based towers or masts and elevating the systems by means of airborne apparatus for covering a relatively larger area is well known to those skilled in the art. For example the concept of tethered balloon antenna systems is taught in such references as British Pat. No. 358,972; U.S. Pat. No. 2,641,756; and U.S. Pat. No. 3,030,500. Additionally, the use of airplanes for providing an airborne antenna platform is taught in U.S. Pat. No. 2,626,348. U.S. Pat.

No. 2,598,064 and U.S. Pat. No. 2,627,021, moreover,

discloses the use of a plurality of aircraft for providing a radio relay system. Finally, the concept of using tethered hovercraft or helicopters for microwave signal SUMMARY The present invention is directed to an improved airborne radiating and receiving antenna system for communications and information transfer or radio, television, telephone, digital data signals, etc. for obtaining not only predetermined ground area coverage, but also a communication common carrier network relay capability over relatively long distances. Briefly, the subject invention is directed to tethered airborne apparatus utilized as a radiating and receiving platform and including means for controlling the height of the airborne apparatus for specific operational requirements. The airborne apparatus is preferably comprised of a lighter than air device such as a balloon under which is mounted a gravity stabilized multiple antenna and transceiver assembly suspended from a universal ball joint subassembly which has a limited freedom of movement. The antenna assembly comprises a plurality of independently rotatable coaxial shafts mounted on a base member attached to the ball joint subassembly, thereby forming a substantially vertically aligned pendulum arm which is adapted to maintainia vertical orientation by means of its own weight. Respective transmitter-receiver means and antenna means are coupled to either end of selected coaxial shafts which additionally include transmission line means for coupling electrical signals therebetween. Each of the selected coaxial shafts and attached antenna means is controlled in azimuth or horizontal plane by means of telemetry control from a ground station which radiates a compass heading signal via a flux gate transmitter to the antenna assembly. A flux gate compass system controls a servo system coupled to each of the selected coaxial shafts to aim the respective antenna means in a predetermined compass direction.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of a system embodying the principles of the present invention;

FIG. 2 is a schematic representation of a long distance communications network providing an air-to-air relay of electrical signals as well as ground station transfer at predetermined intervals;

FIG. 3 is a representation of a typical radiation pattern and network contemplated by the subject invention;

FIGS. 4A and 4B is an elevational view partially in vertical transverse section of a plurality of independently controlled coaxial shafts coupling respective transmitter-receiver means to antenna mounting pads located at the lower extremity thereof;

FIG. 5 is a view of one type of antenna means contemplated for use in combination with the subject invention;

FIG. 6 is a view of a second type of antenna means utilized by the subject invention;

FIG. 7 is a view of yet another type of antenna means utilized by the subject invention;

FIG. 8 is a block diagram of a ground based multiple channel communication transmitter utilized in combination with the subject invention;

FIG. 9 is a block diagram of a ground based multiple channel communication receiver adapted to receive signals from the antenna system contemplated by the subject invention;

FIG. 10 is a block diagram of a typical airborne relay subsystem;

FIG. 1 l is a block diagram illustrative of one airborne receiver apparatus shown in FIG. 10;

FIG. 12 is a block diagram illustrative of one airborne transmitter apparatus shown in FIG. 10; and

FIG. 13 is a block diagram illustrative of another receiver-transmitter apparatus shown in FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings wherein like numerals refer to like parts and more particularly to FIGS. 1 through 3, which is generally illustrative of the inventive concept of the present invention, FIG. 1, inter alia, discloses a pair of lighter than air free space aircraft consisting of tethered balloons 10. It should be observed, however, that this is shown by way of a preferred embodiment only since when desirable other types of tethered airborne apparatus may be utilized as well such as dirigibles, helicopters or even airplanes. Each of the balloons 10 is connected to a tether line or cable 12 which is connected to a winch 14 located on the ground for providing selective altitude control of the balloon l0 and thus provides a variation in antenna platform heights as required for specific geographic locations and/or signal communication requirements. A base member generally illustrated by reference numeral 16 is mounted on the underside of each balloon 10 from which is suspended at multiple antenna assembly 18 which is enclosed within a wind screen 20. The base member 16 is also adapted to include transmitting and receiving apparatus not shown as well as suitable command and control circuitry and the necessary power supplies. Primary electrical power for this apparatus can either be obtained from a respective ground control station 22 coupling power to the airborne base 16 up the tether cable 12 or the balloon itself may additionally include a self-contained electrical power generating system.

Each balloon l and its respective transmitterreceiver apparatus which may be for example a plurality of transceivers adapted to provide an up-down communication link between itself and the control ground station 22 by means of one antenna assembly 26 as well as transmitting and/or receiving signals to and from one or more satellite ground stations 24 within the respective local area, for example area A defined by the radiation pattern of another antenna assembly 28. Additionally, the antenna system 18 is adapted to provide a direct air-to-air communication relay link between an adjacent airborne system similar to itself. This is provided by one or more still other antenna assemblies 29. The ground station 22 is adapted to provide all interface functions with the respective airborne apparatus including directional control of the antenna elements, as well as controlling the overall operation of the receiving and transmission apparatus and the command and control circuitry. This will be considered in detail subsequently.

A balloon l0 tethered at a height h is adapted to electromagnetically radiate and receive information in a substantially circular area (FIG. 3) defined by A 'n'R Information can also be relayed by means of two balloon antenna systems separated by a distance 2R over a distance 4R. 1f the parameter R is considered the line of sight distance, a balloon having an altitude h 10,000 feet, will have a distance R which is in the order of 140 miles. Therefore, local area coverage within the order of 63,000 square miles will be provided while a long line transmission capability with two balloon antennas would be in the order of 550 miles. The following table is more illustrative of typical values for a communication system illustrated in FIG. 1 as compared with a conventional TV transmission tower:

conv. TV station more more more As noted earlier, the ground station 22 provides an up-down" link with the airborne system and performs two functions: (1) controlling the airborne system and (2) transmitting and/or receiving communications signals therebetween. Accordingly, two transmitting and receiving antennas 30 and 32 are located at the particular ground station and are coupled to apparatus, not shown, housed in the station. The satellite stations 24,

however, are shown including but one transmittingreceiving antenna 34. This is because its purpose is primarily for the transfer of communication signals either in single channel or multi-channel configurations; however, when desirable a control function could be added. The satellite stations 24 may be, for example, automotive vehicles having two way mobile phone service,

fixed installations such as schools including educational TV apparatus, police stations, radio-FM-TV stations, or commercial activities providing high speed computer digital information transfer, teletype and/or telephoto transmission as well as any other types of infor mation transfer both in analog and digital modes. It can be seen, therefore, that any desired configuration of balloon locations can be utilized to configure the network either stretched out in length or for encompassing a predetermined closed ground area, both of which are illustrated in FIG. 3.

Referring now to FIG. 2, it is meant to be illustrative of a long line relay network which may stretch, for example, 2,000 miles. The ground station 22 comprising an end terminus 1 for example, can be adapted to couple up to 14 channels of one-way transmission plus the required telemetry and command signals to the balloon 10 which is then relayed to the relay 1 balloon 10 which is also coupled to its respective ground station 22 identified as a local drop insert station No. 1 wherein for example one channel may be dropped or inserted with the required telemetry command as well as including one local monitor channel. The relay number No. 1 is then coupled to any number of relay balloons 10 shown as relay n which is similar in operation to relay number No. 1. Relay n couples to a terminus number 2 balloon 10 at the end of the relay network which then is coupled to the ground station 22 included in terminus number 2 which is substantially identical to terminus number No. 1. Also, two-way transmission between terminus number 1 and terminus number 2 as well as the intermediate relay stations can be mechanized wherein 7 channels, for example, are transmitted in each direction.

Typically a long line video network would include 7 channels transmitting in one direction (west) a band including 7925-81185 MHz while seven channels transmitted in the opposite (east) direction would cover a band of 8124.5 to 8318.0 MHz. Up to seven channels received from the east would cover the band 7300-74935 MHZ while up to seven channels received from the west would cover 74995-76930 MHz. All of these operations would be going on at the same time. The local drop/insert at each balloon relay point would permit local insert in the 7699-77215 MHz range, local drop in the 8324-83465 MHz range, command in the 77275-77500 MHZ range, and monitor in 83525-83750 MHZ range. This network is illustrated for various purposes of illustration only and is not meant to be considered in a limiting sense, since any combination of frequencies or channels can be utilized as desired. Additionally, each of the terminus balloon communications systems can be transformed into relay repeaters simply by reorienting the antenna structure and suitably interconnecting the electronics packages in the airborne equipment by means of the command and control radio link coupling the airborne system to the respective ground control station. A typical ground station transmitting and receiving apparatus adapted for use in a network such as shown in FIG. 2 is disclosed in FIGS. 5 and 6, respectively, and will be treated subsequently.

However, attention is now directed to the free space transmitting and receiving apparatus mounted on the tethered balloon l0 and which is shown in FIGS. 4A and 4B. Referring now to FIG. 4A, the base 16 is secured to the underside of the balloon shown in FIG. 1 and additionally includes a universal ball joint assembly 34 comprised of a spherical member 36 mounted in a ball bearing assembly 38 secured to the

vertical arms

40 and 42 which also form part of the base 16. The center of the sphere 36 is located above the upper contact point of the roller bearing assembly 38 and a pendulum arm member 44 is coupled to the lower surface of the sphere 36 so that it is adapted to hang vertically therefrom due to its own weight as well as the apparatus to be described connected thereto. The weighted pendulum arm 44 is adapted to point downward in the direction of local gravity. A circular rubber damper member 46 is mounted on inwardly facing projections on the end of

arms

40 and 42 which acts as a limit stop for the angle of sway of the pendulum arm 44. The damper 46 is slightly angulated inwardly which in combination with the center of the sphere 36 defines a hypothetical cone having its apex at the center of the sphere. The pendulum arm 44 and the assembly attached thereto is thus gravity stabilized vertically but having a limit determined by the rubber damper member 46 which permits the pendulum to sway within a 45 cone from the vertical which is more than enough motion to allow for continued changes in balloon orientationwith respect to varying wind conditions. Local vertical is maintained by the pendulum to fl within the 45 cone. In addition to acting as a sway limit, the rubber damper member 46 acts as a shock absorber when the pendulum arm tries to exceed this hypothetical 45 cone. The wind screen 20 shown in FIG. 1 provides protection against weather, wind and wind gusts which would otherwise have a tendency to affect the pendulum action or motion of the assembly shown in FIG. 4A. All other forces acting on the pendulum arm 44 provide slow motion changes which are easily compensated as well as the continual changes in wind forces acting on the balloon l0 and its resulting directional motional changes.

Considering now the apparatus attached to the end of the pendulum arm 44, it consists, inter alia, of a mounting ring 48 which is adapted to provide a mounting base for a plurality of concentric independently rotatable cylindrical shaft members. In the specific embodiment, shown in FIGS. 4A and 43, four

shafts

50, 52, 54 and 56 are illustrated; however, it should be noted that any desired number of concentric shafts may be utilized depending upon the desired configuration. These shafts 50 56 moreover are attached to its respective adjacent shaft by means of an intermediate roller bearing assembly which permits independent rotation of each of the shafts about a common longitudinal axis which is in a substantially vertical plane. More specifically, the inner-most shaft 50, which could be considered the base shaft is also rotatable but is supported on a roller bearing assembly 58 by means of a collar 60 threaded onto the upper end of the shaft. The collar 60 is secured to the upper race of the roller bearing assembly 58 while the lower race is secured to a cylindrical frame 62 attached to the mounting ring 48. The frame 62, moreover, is adapted to provide a suspension for the entire multi-shaft assembly including the shafts 50 56. At the lower extremity of the shaft 50 (FIG. 4B) a second roller bearing assembly 64 provides a support for the adjacent shaft 52. The lower race thereof is secured to the shaft 50 while the upper race of the roller bearing assembly 64 is attached to the shaft 52. Additionally, a spacer ring 66 provides a necessary separation from the outer and inner surfaces of the

shafts

50 and 52, respectively. Thus the inner-most shaft 50 is adapted to rotate around its central axis on the

roller bearing assemblies

58 and 64 shown in FIG. 4A and 4B, respectively. Rotation of the shaft 50 is provided by means of a drive motor 66 having its rotor attached to a bevel gear 68 which mates with a beveled ring gear 70 secured to an annular rib member 72 near the upper extremity of the shaft 50. By suitably activating the drive motor 66, selective rotation of the shaft 50 can be provided. The lower extremity of the innermost shaft 50 shown in FIG. 4B terminates in a circular mounting pad 74 which is adapted to receive one or more antennas 76 shown in phantom view but which are shown in greater detail in FIG. 5. The shaft 50 additionally includes a signal transmission line 78 within the cylindrical shaft wall which is adapted to terminate at one end in the antennas 76 and at the other end into an electrical slip ring assembly 80 which couples to an electronic transmitter-receiver apparatus which is shown schematically by reference numeral 82.

In a similar manner, the second inner-most shaft 52 is located on the outside of the shaft 50 by means of the bearing assembly 84 and the roller bearing assembly 64 previously mentioned. The inner race of the bearing assembly 84 is secured to the outer surface of the shaft 50 while the outer race is secured to the upper extremity of shaft 52 which comprises a flared portion to which is attached the beveled ring gear 86. The ring gear 86 couples to the bevel gear 88 which is connected to the shaft of a second drive motor 90. The lower end of the shaft 52 is secured to the upper race of the bearing assembly 64 shown in FIG. 4B and constitutes an annular projection 92 forming an antenna pad to which one or more antennas 94 are adapted to be mounted. It can be seen that the shaft 52 is relatively shorter than the shaft 50 with the mounting pad member 92 shown in FIG. 4B being located above the mounting pad 74. A second independent signal transmission line 96 is lo cated within the side walls of the shaft 52 similar to the transmission lines 78 and terminates in a slip ring assembly 98 which couples into second transmitterreceiver apparatus 100.

Similarly, the two

outer-most shafts

54 and 56 are driven by

respective drive motors

102 and 104 being independently rotated by the bevel and

ring gear assemblies

105 and 106. The concentric shaft

assemblies including shafts

54 and 56 are mutually supported by the bearing

assemblies

107, 108, and 112 in the manner previously noted. The shaft 54 is relatively shorter than shaft 52 while longer than shaft 56. Its lower extremity terminates in an antenna mounting pad 114 and additionally includes a vertically oriented annular ring member 1116 which is adapted to support one or more antennas 118 which are shown in phantom view but are more fully disclosed in FIG. 7.

Shaft 54 also includes an electrical signal transmission line 120 incorporated in the wall thereof which is adapted'to be connected to the antennas 118 as well as terminating in the slip ring assembly 112 which in turn is coupled to a transmitterreceiver apparatus 122. The

outer-most shaft 56 has its lower termination connected to a mounting pad 124 which includes the vertically oriented member 126. This is adapted to provide a mount for one or more antennas 128 which are similar to the antennas 118. Again, a signal transmission line 130 contained in the sidewall of the cylindrical shaft 56 is adapted to couple to the antennas 128 which connects to the slip ring assembly 132 at the upper end of the shaft as shown in FIG. 4A. The slip ring assembly 132 couples into its respective transmitter-receiver apparatus 133 in the same manner that each of the other concentric cylindrical shaft members are adapted to couple respective signal transmission lines contained therein between the antennas mounted at the respective mounting pads to its transmitter-receiver apparatus. Thus, the configuration shown in FIGS. 4A and 4B permit the

antennas

76, 94, 118, and 128 to be selectively oriented in space independently of each other by means of the

respective drive motors

66, 90, 102 and 104. Since the entire antenna assembly thus described is suspended from the mounting ring 48 attached to the pendulum arm 44, the weight of the assembly provides the required vertical stabilization while the drive motors produce aiming of the antenna members coupled to the shafts in the horizontal or azimuth direction.

Before continuing further, attention now is directed to FIGS. 5, 6 and 7, which are typically illustrative of the antennas utilized in combination with the assembly shown in FIGS. 4A and 48. For example, FIG. is illustrative of the antenna configuration mounted on the lowermost pad 74 shown in FIG. 4B and which is part of the cylindrical shaft 50. The antennas 76 comprise spiral antenna elements attached to the bottom surface of pad 74 by means of the antenna base elements 134 secured to the pad 74 by means of suitable hardware such as a nut and bolt. Each of the spiral antenna elements 76 is commonly coupled to the transmission line 78 shown in FIG. 4B and are directed downward in a substantially vertical orientation. This is for purposes of being pointed directly at the ground station 22 shown in FIG. 1. Thus the antenna elements 76 form one element of an air-to-ground or up-down" link for electrical signals coupled between the ground station 22 and the electronic apparatus 82 shown in FIG. 4A. Spiral antennas are preferred for the up-down or air-toground link because such antennas have wide beamwidth and permit the ground station command and control equipment to be located at a remote distance from the ground tethering point. Furthermore, a high gain antenna is not required and the spiral antenna is very light in weight. The number of spiral antennas required depend upon the number of channels of communication being established between the ground station 22 and the airborne electronics system.

Referring now to FIG. 6, there is disclosed the preferred embodiment of the antenna shown by reference numeral 94 in FIG. 4B and which constitutes the antenna assembly for local radiation coverage between the airborne system and the satellite stations 24 shown in FIG. 1. The antenna configuration shown in FIG. 6 comprises the slightly tapered reflector element 138 secured to a swival base 140 attached to an arm 142 mechanically connected to the pad 92 by suitable hardware. The swival connection between the base 140 and the arm 142 permits adjustment of the directivity of the reflector 138. Additionally an antenna feed member 144 is included which is adapted to be connected to the transmission line 96 shown in FIG. 48. Such an antenna provides a gain of approximately 2dbm and permits information transfer in a substantially circular downward hemispherical radiation pattern. Simultaneous multichannel wideband and narrow band information in both transmission and receiving modes can be handled by this type of an antenna.

Considering now the antenna means utilized for the long line or relay type transmission and reception between airborne stations, reference is made to FIG. 7 which discloses such apparatus. The antenna disclosed therein is typical of either of the antennas shown by

reference numeral

118 or 128 shown in FIG. 4B and comprises a section of a parabolic cylinder shown by reference numeral 146 coupled to the respective

vertical support element

116 or 126. The parabolic cylinder design is preferred because the antenna gain and bandwidth are the same as a parabolic antenna of similar diameter, however its main purpose is that the main beam is not attenuated. There is a beamwidth reduction in the vertical plane; however, this disadvantage is disregarded since the antenna pointing direction will be substantially in the horizontal plane. The parabolic cylinder antenna size in the parabolic dimension is determined by the beamwidth desired and the gain requirements of the system. An antenna having a gain in the 23-25dbm range is desirable. The following Table II is illustrative of the power gain in the effective area of other types of antenna configurations which might be utilized when desired.

TABLE II Antenna Type Gain Above Effective Isotropic Area Radiation Isotropic Radiation 1.0 V/4 1r Infinitesimal dipole or loo 1.5 1.5)3/4 1r Half wave dipole 1.64 l.64)./4 1r Optimum horn (mouth area=A) l0 Al). 0.81 A Horn (max. gain for fixed length mouth area A) 5.6Al). 0.45 A Parabola or metal lens 6.3-7.5 All. 0.5-0.6 A Broadside array (area=A) Billboard" 4-rrA/).(max) A (max) Omnidirectional stacked array (length-L, stack interval l.) =2L/l. LA/Z 1r Referring now back to FIGS. 4A and 4B the ground station 22 (FIG. 1) is electromagnetically coupled to the airborne system by means of the antenna 76. The ground station is intended to serve as the master command and control for the entire airborne system attached to the respective balloon. These functions include the necessary electrical, mechanical and opera tional control of the system which includes among other things, steering and directional control of each of the antenna mounts including the respective cylindrical coaxial shaft and the intercoupling of information between selective antennas and the respective transmitter-receiver apparatus coupled thereto. Thus the ground station selectively intercouples the airborne antenna structure according to the specific requirements of the respective location. More particularly, all signals directed to and from the ground station 22 are coupled to and from the transmitter-receiver apparatus, of predetermined type signals, 82 by means of the transmission line 78 and the slip ring assembly 80. For example, signals transmitted to the airborne system appear at circuit means 146 which is coupled to a command and control assembly 150 mounted on the base 16 by means of an input harness assembly shown by reference numeral 148. The command and control assembly 150 as well as the electronics apparatus attached to the mount 48 is adapted to receive suitable power supply potentials from a power supply attached to the base 16. The command and control assembly 150 is adapted to selectively interconnect the

transmitterreceiver apparatus

82, 100, 122 and 133 by means of an output harness 149 as well as coupling directional control signals for each of the antenna shafts which have been received from the ground station 22 by means of the apparatus 82.

Independent directional or compass heading control of each antenna assembly including the

antennas

76, 94, 118 and 128 is maintained by respective servo control systems shown diagrammatically by

reference numerals

152, 154, 156 and 158 coupled to the

drive motors

66, 90, 102 and 104. Each of the servo systems 152 158 is coupled to a respective flux gate compass system and synchro control transformer shown generally by

reference numerals

160, 162, 164 and166 attached to the mounting ring 48 and which receive inputs from respective flux gate transmitter apparatus shown schematically by reference numeral 49 located at the ground station 22. A flux gate transmitter and compass system is well known to those skilled in the art, an example of which is the Bendix type 15026. The flux gate transmitter on the ground provides the heading signal which is coupled to the flux gate compass by means of the transceiver 82 and the command and control assembly 150. The desired respective headings are manually set on the ground. Deviations in heading relative to magnetic North develop a signal voltage proportional in level and phase to the deviation from the magnetic North. These control signals actuate the servo system connected to its respective drive motor which will rotate the concentric shaft to which it is coupled to the proper heading in azimuth. A system of this type is easily able to control the directivity within :2. Thus each of the concentric cylindrical shafts 50 56 are independently oriented by means of the flux gate compass system 160 166 which receive individual heading signals from the ground station.

Having thus selectively oriented each of the four antenna structures from the ground station 22, the updown link sends telemetric control signals to the command and control assembly 150 for controlling the transmission and reception to and from the

transmitterreceiver apparatus

82, 100, 122 and 133. For example,

apparatus

122 and 133 may be interconnected such that the antennas 128 coupled to the apparatus 133 are adapted to receive signals which are then coupled to apparatus 122 for transmission from antennas 118 in a long-line" relay communications such as shown in FIG. 10. A more detailed illustrative embodiment is shown in FIGS. 11 13. A local area communication signal for the surrounding line of sight coverage of the airborne system is coupled to and from the apparatus 100 which is coupled to the antennas 94. Any desired combination of interconnections can be made under the control of the ground station 22 via the up-down link including the transmitter-receiver 82 and the command and control assembly 150. The configuration shown in FIG. 4A and 45 provides a very flexible communications system having a multi-channel flexibility with diversity of operation as well as individual selective orientation of each antenna configuration of the assembly as controlled from the ground station.

In order to more fully understand the information transfer contemplated by the subject invention, FIGS. 8 and 9 are illustrative of a typical multi-channel communications transmitter and receiver, respectively, adapted for use in combination with the apparatus shown in FIGS. 4A and 4B. The ground station transmitter shown in FIG. 8 discloses a seven channel configuration with means provided for transforming it into a fourteen channel configuration when desirable. Each input signal is coupled to a respective input terminal 168-1 168-7. Considering for example channel 1, the input signal is applied to a wide band modulator 170-1 such as a spread spectrum generator or a video frequency UHF transmitter which produces a modulated output signal of for example a 70MI-Iz. This signal is immediately mixed with a local oscillator frequency of for example 544MHz applied from crystal oscillator 171 shown in FIG. 9 in a mixer 172-1 which produces a working IF frequency of for example, 614MHz. The IF signal is applied to a narrow band filter 174-1 to reject the local oscillator frequency and the image frequencies. The output of the narrow band filter 174-1 is next applied to an IF amplifier 176-1 which provides a gain of, for example, +l3db. The amplifier IF signal is then mixed with a second local oscillator signal in the mixer 178-1 coupled from a synthesizer circuit 177 shown in FIG. 9 to transform the 614MHz IF signal to an X-band RF frequency desired for the specific channel i.e. channel 1. The other channels 2 through 7 would provide a different X-band local oscillator RF frequency as determined by the synthesizer outputs. The X-band output of the mixer 178-1 is passed through an isolator 180-1 which provides an impedance match between the mixer 178-1 and a second narrow band filter 182-1. The narrow band filter 182-1 rejects the second local oscillator frequency and the image frequencies. The channel 1 X-band signal is now fed to a power amplifier 184-1 which may be, for example, a traveling wave tube (TWT) amplifier which has an approximate net gain of +50db. Following the TWT power amplifier 184-1, the X-band signal is passed through a third narrow band filter 186-1 to reject noise amplified by the traveling wave tube 184-1. Following the narrow band filter 186-1, an isolator 188-1 and low pass filter 190-1 couple into an antenna feed 192-1 of a parabolic cylindrical antenna 194. Since seven input feeds 192-1 192-7 are illustrated, a system configuration comprised of 14 channels would couple into the other seven input feeds by means of a circulator 196-1 196-7 coupled intermediate the narrow band filter 186 and the isolator 188. In either configuration, the isolator 188-1 reduces the cross coupling between antenna feeds and the low pass filter 190-1 rejects channel harmonics. Thus what has been shown is a seven or 14 channel X-band RF- transmitter which is adapted to radiate RF signals to the airborne system via the updown" link antennas 76 for distribution by the command and control assembly 150 for coupling to one or more of the transmitter-receive apparatus respectively associated with the

antennas

94, 118 or 128, as shown in FIGS. 4A and 4B.

. Referring now to FIG. 9, the frequency synthesizer 177 is additionally adapted to provide the local oscillator frequencies for the receiver circuitry shown therein.

FIG. 9 also discloses a second crystal oscillator 198 which is adapted to provide a fixed frequency of, for example, 684MHz, and which will be discussed subsequently.

Directing attention now more particularly to the receiver apparatus shown in FIG. 9, a parabolic antenna 204 having a gain in the range of 28db and a beamwidth of 6 is adapted to receive, for example, 14 separate channel RF signals in the X-band range which are fed to a wideband filter 206 and then to a' low noise RF amplifier 208 having an approximate gain of 35db and a noise figure of 6.5db. These signals are then passed through a second wideband filter 210 which is adapted to reject the noise due to the image frequencies. Following the wideband filter 210 an isolator 212 couples the X-band signals into a mixer 214 which is adapted to receive an X-band to S-band local oscillator signal from the synthesizer 177. The output of the mixer 214 comprises 14 channels of S-band frequencies which are fed into a 14 way power splitter 216. Seven of the outputs are terminated in substantially identical resistive load impedances 218 while the remaining 7 signals are fed to seven separate channel circuits. Each receiver channel circuit, for example channel 1, includes a narrow band filter 220-1 which is adapted to have a MI-Iz bandwidth for one channel of S-band frequency while rejecting the adjacent channel center frequency by not less than 35db. The output of the narrow band filter 220-1 is fed to a 24db IF amplifier 222-1. The output of the IF amplifier 222-1 is applied to the mixer 224-1 which receives a S-band to UHF local oscillator signal from the synthesizer 177, which produces a working IF frequency of for example, 614MHz. This IF signal is passed through a 3db matching pad 226-1 and then to a second narrow band filter 228-1 which rejects the local oscillator frequencies. The 614MHz UHF IF frequency is next amplifier by an IF amplifier 230-1 including automatic gain control (AGC). The output of the IF amplifier 230-1 is next coupled to a second mixer 232-1 through a 6db matching pad 234-1. The mixer 232-1 receives either a 544MHz signal from the crystal oscillator 171 or a 684MHz signal from the crystal oscillator 198 coupled thereto through a switch 200. The 554MHz signal applied to the switch 200 is identified as the NOR or normal receive signal while the 684MHz signal is labeled the INV or invert signal, for purposes of which will be explained subsequently. The output of the mixer 232 provides an IF signal which is in the range of 70MHz, which is applied to a suitable demodulator circuit 238-1 through a low pass filter 240-1. The output of the demodulator 238 appears at terminal 242-1 and constitutes the desired output signal.

In the event that it is desired to relay certain types of information such as spread spectrum signals which require non-inversion of the signals, these signals would undergo an odd number of hops or inversions from every other ground local drop/insert station to the ground terminus shown in FIG. 2, and would therefore be inverted. In order to maintain proper polarity of the received signals, the two

crystal oscillators

171 and 198 are utilized which are adapted to be 70MHz below and 70M Hz above respectively the working IF frequency of 614MHz. The proper LO frequency is selected by means of the switch 236. It should be pointed out, however, that in signal transmission, this facility is not required and therefore only a single frequency, i.e.

544MHz is applied to the apparatus shown in FIG. 8 from the crystal oscillator 171. In an asymmetrical system, however, where more than 7 channels are to be received, the additional receiving channels which are adapted to be coupled to the power splitter 216, rcplace the load resistors 218 shown.

It should be pointed out that the frequencies provided by the synthesizer 198 depend upon the desired system configuration. For example, 14 transmitters require one set of local oscillator frequencies while the 14 receiver circuits require a different set of local oscillator frequencies and an odd number of hops between terminus stations will require a different set of transmitter or receiver local oscillator frequencies.

Referring now to FIG. 10, there is disclosed therein a typical airborne long-line relay subsystem incorporating the apparatus shown in FIGS. 4A and 4B which for example utilizes the antennas 128 as the receiving antennas and the antennas 118 as the transmitting antennas. Each of the antennas respectively are coupled to the transmitter-

receiver apparatus

134 and 122 each of which includes receiver apparatus shown more particularly in FIG. 11 and transmitter apparatus which is shown more particularly in FIG. 12 and wherein both apparatus includes up to fourteen channels. The respective receiver and transmitter elements contained in each of the transmitter-

receiver apparatus

122 and 133 is innerconnected through the command and control assembly so that proper innerconnection can be made for selectively utilizing either the receiver or the transmitter portions of the

apparatus

133 and 122. A synthesizer 202 is also included for providing at least five local oscillator frequencies for proper operation of the subsystem. Additionally, the up-down transmitter-receiver apparatus 82 connected to the spiral antenna means 76 is also coupled into the command and control assembly 150 and includes apparatus for providing one local drop channel, one or two insert channels plus one monitoring channel which is shown in more detail in FIG. 13.

The receiver portion of the airborne

transmitterreceiver apparatus

122 and 133 shown in FIG. 11 is identical to the ground terminus receiver means shown in FIG. 9 from the wideband filter 206 up to the IF amplifier 230 having AGC for the channels 1 through 7. Considering channel 1 for purposes of illustration the output of the IF amplifier 230-1 in FIG. 11 is fed into a two-way power splitter 242-1, the outputs of which are coupled to two identical matching pads 244-1 and 246-1. The signal from the pads 244-1 is fed to the command and control assembly 150 for coupling to transmitter apparatus shown in FIG. 12 while the output from the pad 246-1 is adapted to be coupled to a l X 14 RF switch 248 coupled to the monitor and telemetry channel in the up-down" transmitter-receiver apparatus shown in FIG. 13.

With respect to the airborne transmitter apparatus shown in FIG. 12, it is substantially identical to the ground based transmitter shown in FIG. 8 from the first IF amplifiers 176-1 176-7 to the low pass filters -1 190-7 which couple to the respective radiating antenna. It is to be noted that the input to the respective IF amplifiers 176-1, etc. are coupled back to the command and control assembly for innerconnection to the airborne receiver apparatus shown in FIG. 11 and briefly described above. The synthesizer 202 is adapted to couple the required local oscillator frequencies as shown in FIGS. 11 and 12 so that multi-channel signal input and output translation occurs between the

antenna

128 and 118 as shown in FIG. 10.

Referring now to FIG. 13, there is disclosed the airborne up-down transmitter-receiver apparatus 82 noted in FIG. as well as FIG. 4A. It includes circuit means for providing a local drop channel,a local insert channel, and a monitor and telemetry channel to the ground station via the spiral antenna means 76. Considering first the local drop channel, it comprises apparatus substantially identical to the airborne transmitter apparatus shown in FIG. 12 and is shown comprising the elements 176' 190' which includes the apparatus from the IF amplifier to the low pass filter. The input to the IF amplifier 176 is selectively coupled to one of the seven channel signals appearing at a selected output pad 246-1 246-7 which is coupled thereto through the command and control assembly 150. The channel signal to be dropped to the ground station is coupled to the antenna means 76 from the low pass filter 190.

The local insert channel apparatus shown in FIG. 13 is substantially identical to the airborne receiver apparatus shown in FIG. 12 with the exception that the

wideband filters

206 and 210 have been replaced by

narrow band filters

207 and 209. Also in place of the 14 way power splitter 216 shown in FIG. 11 the apparatus shown in FIG. 13 employs a two way power splitter 215, one output of which is fed to the narrow band filter 220 while the other output is coupled to a narrow band filter 250 which couples into a mixer 252 which receives a command local oscillator frequency from the synthesizer 202. The output of the mixer 252 is fed into another narrow band filter 254 and then into an amplifier 256. The output of the amplifier 256 is coupled into a limiter and discriminator 258 for obtaining command signals which are fed to a logic circuit 260 which couples into the command and control assembly150. The insert signal which is fed to the amplifier 230 and the pad 246 is coupled into the command and control assembly 150 for selective coupling to one of the airborne transmitter inputs shown in FIG. 12.

The command information which is decoded in the logic 250 and fed into the command and control assembly 150 feeds back a control signal to the l X 14. RF switch 248 by means of a circuit lead 262 which selectively controls the RF switch to select one of the channel inputs from the airborne receiver apparatus shown in FIG. 11. The output is then coupled into transmitter circuitry 176" 190" which is substantially identical to the airborne transmitter apparatus shown in FIG. 12 with the exception that a coupler 262 is adapted to insert a telemetry signal coupled thereto from telemetry logic circuitry contained in the command and control assembly 150. This signal is applied through a modulator circuit 264, a mixer 266 which receives a telemetry local oscillator frequency from the synthesizer 202 and an IF amplifier 268. Thus the monitor and telemetry channel'apparatus is adapted to couple information from the low pass filter 190" to the spiral antenna means 76 for transmission to the ground station.

What has been shown and described, therefore, is a multi-channel airborne transmitting and receiving station mounted on the underside of a tethered balloon and controlled from a ground station which serves as the master command and control for the entire system which includes controlling the electrical, mechanical and operational parameters of the entire system, in-

' has been shown with a certain degree of particularity,

for purposes of illustration only, the system disclosed is adapted to operate in any desired mode or frequency range of electromagnetic signal transmission and reception. Not only is the system adapted to handle multi-channel X-band signal transmission as shown in FIGS. 8 13, but is also adapted to handle standard AM and FM radio broadcasting as well as television transmission wherein amplitude modulation of one carrier is utilized for video transmission while the audio transmission occurs as FM modulation of a second carrier. In addition selective types of UHF and VHF operation can also be mechanized. Other types of information handling are also contemplated e.g., telegraphy, telephony, facsimile, multichannel multiplex voice frequency telegraphy, and analog/digital computer data, etc.

Many other network combinations are adapted to be configured utilizing the teachings of the subject invention which eliminate the need for telephone poles, telephone lines, cables, microwave towers and the usual elements involved in a conventional information transfer network. The present system, moreover, can tie into any existing conventional network or information distribution system. For undeveloped geographic areas, the present invention is particularly useful in that it permits an advance modern complex information handling and distribution network system to be provided in a very short time and at a very low cost. Furthermore, simple conventional low cost electrical elements can be utilized in assembling of a ground satellite station such that equipment costs are comparable to normal high quality roof top mounted and driven antennas or a receiver elements in home use at present. This represents a substantial reduction in network cost and user cost over present systems and provides a signal quality that is technically of higher grade than with existing systems due to the fact that no land line routing or multiswitching operations within the land routing network are involved which inherently degrade information quality. Direct transmission via the air-to-air relay link maintains clean and undisturbed electromagnetic signals to its final destination.

Having thus described the present invention with what is considered at present to be the preferred embodiment of the subject invention, I claim as my invention:

1. A system for receiving and transmitting electromagnetic radiation including various types of radio signals, TV signals as well as other types of information and/or data communication signals, comprising, in combination:

airborne apparatus for providing a mounting platform for electronic transmitting and receiving apparatus;

a gravity stabilized antenna assembly suspended from said airborne apparatus, said antenna assembly being comprised of (a) a mounting base attached to the underside of said airborne apparatus including a ball-joint housing depending therefrom, said housing having a downwardly depending side portion and a lower end portion having a circular means, and (3) a communication air-toair relay link along a substantially horizontal direction by at least one-of yet another of said antenna means.

opening therein, said side portion also including an inwardly projecting ball bearing mount intermediate its length and a tapered race type ball bearing assembly having a concave bearing surface affixed thereto, a spherical member of predetermined di- 4. The invention as defined by claim 1 wherein said ameter resting on said concave bearing surface, directional control meansincludesaflux gate transmitsaid diameter being of such a magnitude that the ter at said ground station for providing a compass headcenter of the sphere is located above the uppering signal for each of said antenna means via said upmost contact point between the spherical member down link and wherein each of said selected coaxial and the ball bearing assembly, said opening addishafts is coupled to a flux gate compass system and adtionally having an inwardly angulated circular ditionally including means responsive to the output of damper member affixed thereto the outer surface said compass system to rotate said shaft in a predeterof which defines a hypothetical cone having an mined direction in accordance with said compass headapex at the center of said spherical member, (b)'a ing signal.

pendulum arm member attached to one extremity 5. The invention as defined by claim 4 wherein said to said spherical member and projecting through last-recited means comprises an electrical drive motor said damper member and being suspended there- 29 and an electrical servo system coupled between said from in substantially vertical alignment, (c) a supflux gate compass system and said drive motor for conport member attached to the other extremity of trolling the operation of said drive motor.

said arm member, and (d) a plurality of coaxial cy- 6. The invention as defined by claim 1 wherein said lindrical shafts which are independently rotatable signal transmitter-receiver apparatus includes means about the central longitudinal axis thereof mounted for multi-channel electrical signal communications. on said support member and wherein selected 7. In an electromagnetic signal communication sysshafts of said plurality of shafts each additionally tem,

includes separate electrical signal transmission line a plurality of tethered aircraft disposed at predeter- 2. The invention as defined by claim 1 wherein said 5 airborne apparatus comprises a lighter than air vehicle.

3. The invention as defined by claim 2 wherein said lighter than air vehicle comprises a balloon.

means carried by the respective shaft side wall for by means of at least one of said antenna means, (2) a transmitting and receiving link for a local ground area coverage by at least one other of said antenna mined heights above the surface of the earth in coupling electrical signals from one end of the re- 30 order to provide respective free space antenna spective shaft to substantially the opposite end platforms for electronic signal receiving and transthereof; mitting apparatus; respective antenna means mounted at said one end of a ground based receiving and transmitting station losaid selected coaxial shafts and being coupled to cated beneath each of said aircraft and including said respective transmission line means; means for controlling the aircraft and means for a ground station for controlling said airborne apparatransmitting and receiving a plurality of electrical tus; signals to and from the respective aircraft and antenna directional control means coupled to said means for transmitting at least a first and a second selected coaxial shafts for properly pointing the recontrol signal thereto; spective antenna means in a predetermined comeach of said aircraft additionally including a multiple pass heading in a substantially horizontal plane, antenna structure comprising a pendulum type said control means including a telemetry control gravity stabilized antenna mount comprised of (a) radio link with said ground station whereby each a mounting base attached to the underside of said antenna means is independently oriented in reairborne apparatus including a ball-joint housing sponse to a compass heading signal transmitted to depending therefrom, said housing having a downsaid control means from said ground'station; wardly depending side portion and a lower end porrespective electrical signal transmitter-receiver appation having a circular opening therein, said side ratus located on said airborne apparatus and couportion also including an inwardly projecting ball pled to said antenna means and additionally includbearing mount intermediate its length and a taing respective electrical slip ring assemblies intepered race type ball bearing assembly having a congral with said selected shafts, coupled to the oppocave bearing surface affixed thereto, a spherical site end of said respective transmission line means; member of predetermined diameter resting on said and concave bearing surface, said diameter being of electrical signal command and control apparatus, 10- such a magnitude that the center of the sphere is cated on said airborne apparatus, coupled to each located above the uppermost contact point beof said signal transmitter-receiver apparatus for setween the spherical member and the ball bearing lectively controlling the operation of the respective assembly, said opening additionally having an insignal transmitter-receiver apparatus to provide, wardly angulated circular damper member affixed (1) an up-down" communication link with said thereto the outer surface of which defines a hypoground station including the transfer of command thetical cone having an apex at the center of said and control signals therefrom as well as the transfer spherical member, (b) a pendulum arm member of communications signals on one or more commuattached at one extremity to said spherical member nications channels to said airborne apparatus inand projecting through said damper member and cluding said signal transmitter-receiver apparatus being suspended therefrom in substantially vertical alignment, (c) a support member attached to the other extremity of said arm member, and (d) a plurality of coaxial shafts attached to and suspended from said antenna mount in a substantially vertical direction and including electrically controlled means for independently rotating a selected number of said shafts about the center longitudinal axis thereof, said selected number of said coaxial shafts each additionally including separate transmission line means mounted within the respective shaft side wall and extending substantially between each end thereof, antenna means attached to the lower extremity of said selected number of coaxial shafts and coupled to the respective transmission line means,

independent transmitter-receiver means and slip ring coupling means integral with said selected shafts coupled to the respective transmission line means at the other end of the respective shaft for receiving or transmitting signals to the respective antenna means;

means coupled to said selected number of coaxial shafts for rotating each shaft independently to the predetermined azimuth direction in accordance with a compass setting transmitted from said ground station via said first control signal transmitted from said ground station whereby at least one antenna means is directed toward said ground station, at least one other antenna means directed toward a predetermined local area under the respective aircraft as determined by the subtended radiation pattern of the antenna means, and at least one still another antenna means is directed toward another tethered aircraft of said plurality of aircraft; and

circuit means located on each said aircraft, being responsive to said second control signal transmitted from said ground station to selectively operate each said transmitter-receiver means to relay communication signals between adjacent tethered aircraft and 'to provide communication signal transfer between the respective ground stations and aircraft.

8. The invention as defined by claim 7 wherein said plurality of aircraft are comprised of lighter than air balloons and wherein said ground station additionally includes means for controlling the height of the respective balloons as well as means for monitoring the condition thereof.

9. The invention as defined by claim 8 wherein said first recited means comprises a tether cable and wherein said tether cable includes means for coupling electrical power from said ground station to said antenna platform.

10. The invention as defined by claim 7 wherein said at least one of said antenna means comprises a first type antenna, said at least one other antenna means comprises a second type antenna, and said at least one yet another antenna means comprises a third type antenna.

11. The invention as defined by claim 10 wherein said first type antenna comprises a spiral antenna, said second type antenna comprises a dish type antenna, and said third type antenna comprises a parabolic cylindrical type antenna.

12. The invention as defined by claim 7 wherein said means for transmitting and receiving a plurality of electrical signals comprises a multi-channel transmitter and a multichannel receiver of microwave signals.

13. The invention as defined by claim 12 and additionally including a frequency synthesizer coupled to said transmitter and said receiver for respectively coupling at least one local oscillator signal thereto for generating an IF signal.

Claims

1. A system for receiving and transmitting electromagnetic radiation including various types of radio signals, TV signals as well as other types of information and/or data communication signals, comprising, in combination: airborne apparatus for providing a mounting platform for electronic transmitting and receiving apparatus; a gravity stabilized antenna assembly suspended from said airborne apparatus, said antenna assembly being comprised of (a) a mounting base attached to the underside of said airborne apparatus including a ball-joint housing depending therefrom, said housing having a downwardly depending side portion and a lower end portion having a circular opening therein, said side portion also including an inwardly projecting ball bearing mount intermediate its length and a tapered race type ball bearing assembly having a concave bearing surface affixed thereto, a spherical member of predetermined diameter resting on said concave bearing surface, said diameter being of such a magnitude that the center of the sphere is located above the uppermost contact point between the spherical member and the ball bearing assembly, said opening additionally having an inwardly angulated circular damper member affixed thereto the outer surface of which defines a hypothetical cone having an apex at the center of said spherical member, (b) a pendulum arm member attached to one extremity to said spherical member and projecting through said damper member and being suspended therefrom in substantially vertical alignment, (c) a support member attached to the other extremity of said arm member, and (d) a plurality of coaxial cylindrical shafts which are independently rotatable about the central longitudinal axis thereof mounted on said support member and wherein selected shafts of said plurality of shafts each additionally includes separate electrical signal transmission line means carried by the respective shaft side wall for coupling electrical signals from one end of the respective shaft to substantially the opposite end thereof; respective antenna means mounted at said one end of said selected coaxial shafts and being coupled to said respective transmission line means; a ground station for controlling said airborne apparatus; antenna directional control means coupled to said selected coaxial shafts for properly pointing the respective antenna means in a predetermined compass heading in a substantially horizontal plane, said control means including a telemetry control radio link with said ground station whereby each antenna means is independently oriented in response to a compass heading signal transmitted to said control means from said ground station; respective electrical signal transmitter-receiver apparatus located on said airborne apparatus and coupled to said antenna means and additionally including respective electrical slip ring assemblies integral with said selected shafts, coupled to the opposite end of said respective transmission line means; and electrical signal command and control apparatus, located on said airborne apparatus, coupled to each of said signal transmitterreceiver apparatus for selectively controlling the operation of the respective signal transmitter-receiver apparatus to provide, (1) an ''''up-down'''' communication link with said ground station including the transfer of command and control signals therefrom as well as the transfer of communications signals on one or more communications channels to said airborne apparatus including said signal transmitter-receiver apparatus by means of at least one of said antenna means, (2) a transmitting and receiving link for a local ground area coverage by at least one other of said antenna means, and (3) a communication air-to-air relay link along a substantially horizontal direction by at least one of yet another of said antenna means.

2. The invention as defined by claim 1 wherein said airborne apparatus comprises a lighter than air vehicle.

4. The invention as defined by claim 1 wherein said directional control means includes a flux gate transmitter at said ground station for providing a compass heading signal for each of said antenna means via said ''''up-down'''' link and wherein each of said selected coaxial shafts is coupled to a flux gate compass system and additionally including means responsive to the output of said compass system to rotate said shaft in a predetermined direction in accordance with said compass heading signal.

5. The invention as defined by claim 4 wherein said last-recited means comprises an electrical drive motor and an electrical servo system coupled between said flux gate compass system and said drive motor for controlling the operation of said drive motor.

6. The invention as defined by claim 1 wherein said signal transmitter-receiver apparatus includes means for multi-channel electrical signal communications.

7. In an electromagnetic signal communication system, a plurality of tethered aircraft disposed at predetermined heights above the surface of the earth in order to provide respective free space antenna platforms for electronic signal receiving and transmitting apparatus; a ground based receiving and transmitting station located beneath each of said aircraft and including means for controlling the aircraft and means for transmitting and receiving a plurality of electrical signals to and from the respective aircrafT and means for transmitting at least a first and a second control signal thereto; each of said aircraft additionally including a multiple antenna structure comprising a pendulum type gravity stabilized antenna mount comprised of (a) a mounting base attached to the underside of said airborne apparatus including a ball-joint housing depending therefrom, said housing having a downwardly depending side portion and a lower end portion having a circular opening therein, said side portion also including an inwardly projecting ball bearing mount intermediate its length and a tapered race type ball bearing assembly having a concave bearing surface affixed thereto, a spherical member of predetermined diameter resting on said concave bearing surface, said diameter being of such a magnitude that the center of the sphere is located above the uppermost contact point between the spherical member and the ball bearing assembly, said opening additionally having an inwardly angulated circular damper member affixed thereto the outer surface of which defines a hypothetical cone having an apex at the center of said spherical member, (b) a pendulum arm member attached at one extremity to said spherical member and projecting through said damper member and being suspended therefrom in substantially vertical alignment, (c) a support member attached to the other extremity of said arm member, and (d) a plurality of coaxial shafts attached to and suspended from said antenna mount in a substantially vertical direction and including electrically controlled means for independently rotating a selected number of said shafts about the center longitudinal axis thereof, said selected number of said coaxial shafts each additionally including separate transmission line means mounted within the respective shaft side wall and extending substantially between each end thereof, antenna means attached to the lower extremity of said selected number of coaxial shafts and coupled to the respective transmission line means, independent transmitter-receiver means and slip ring coupling means integral with said selected shafts coupled to the respective transmission line means at the other end of the respective shaft for receiving or transmitting signals to the respective antenna means; means coupled to said selected number of coaxial shafts for rotating each shaft independently to the predetermined azimuth direction in accordance with a compass setting transmitted from said ground station via said first control signal transmitted from said ground station whereby at least one antenna means is directed toward said ground station, at least one other antenna means directed toward a predetermined local area under the respective aircraft as determined by the subtended radiation pattern of the antenna means, and at least one still another antenna means is directed toward another tethered aircraft of said plurality of aircraft; and circuit means located on each said aircraft, being responsive to said second control signal transmitted from said ground station to selectively operate each said transmitter-receiver means to relay communication signals between adjacent tethered aircraft and to provide communication signal transfer between the respective ground stations and aircraft.